This invention relates generally to improvements in external or exoskeletal prosthetic devices and systems of the type utilizing an implanted, bone anchored mounting post having or carrying an externally protruding or externally exposed fixator structure for removable attachment to a prosthesis such as a prosthetic limb or the like. More particularly, this invention relates to an improved attachment system for coupling the external fixator structure to the prosthesis, wherein the attachment system includes a safety release mechanism adapted to release in response to an excess mechanical load applied to the prosthesis.
Socket type prosthetic limbs such as prosthetic arm and leg structures for use by amputees are generally well known in the art, wherein a prosthesis is constructed with an open-ended and typically padded socket structure for receiving and supporting the post-surgical stump of an amputated limb. By way of example, a socket type prosthetic leg includes such open-ended socket structure at an upper end thereof for receiving and supporting the post-surgical upper leg of a transfemoral amputee. Various straps and/or other fasteners are provided for securing the prosthetic leg to the amputated limb to accommodate walking mobility at least on a limited basis. Such prosthetic limbs can be an important factor in both physical and mental rehabilitation of an amputee.
However, socket type prosthetic limbs are associated with a number of recognized limitations and disadvantages. In particular, the socket style prosthesis inherently couples mechanical loads associated with normal ambulatory activity through a soft tissue interface defined by the soft tissue covering the end or stump of the amputated limb, but wherein this soft tissue interface is structurally unsuited for this purpose. While many different arrangements and configurations for the requisite straps and other fasteners have been proposed for improved transmission and distribution of these mechanical loads to bone structures to achieve an improved secure and stable prosthesis attachment, to correspondingly accommodate a more natural ambulatory movement, such arrangements have achieved only limited success. In addition, compressive loading of the soft stump tissue interface often results in blisters, sores, chafing and other undesirable skin irritation problems which have been addressed primarily by adding soft padding material within the socket structure. But such soft padding material undesirably increases the extent of the soft or non-rigid interface between the amputated limb and prosthesis, all in a manner that is incompatible with an optimally secure and stable prosthesis connection. As a result, particularly in the case of a prosthetic leg, traditional socket style connection structures and methods have generally failed to accommodate a normal walking motion.
In recent years, improved external or exoskeletal prosthetic devices have been proposed, wherein the external prosthesis is structurally linked by means of a bone anchored mounting system directly to patient bone. In such devices, a rigid mounting post is surgically implanted and attached securely to patient bone as by means of osseointegration or the like. This implanted bone anchored mounting post extends from the bone attachment site and includes or is attached to a fixator pin or post structure that protrudes through the overlying soft stump tissue at the end of the amputated limb. Thus, one end of the fixator structure is externally exposed for secure and direct mechanical attachment to a prosthetic limb or the like by means of a rigid linkage.
In such bone anchored mounting systems, mechanical loads on the prosthetic limb during ambulation are thus transmitted by the rigid linkage and through the external fixator structure and implanted mounting post directly to patient bone. As a result, conventional and undesirable mechanical loading of the soft tissue interface is avoided, and substantially improved and/or substantially normal patient movements are accommodated. In addition, the requirement for compressive loading of the soft tissue at the end of the amputated limb is significantly reduced, to correspondingly reduce incidence of blisters and other associated skin irritation problems. Moreover, by mechanically linking and supporting the prosthesis directly from patient bone, amputees have reported a significant increase in perception of the prosthesis as an actual and natural body part—a highly desirable factor referred to as “osseoperception”.
Although use of a bone anchored mounting system offers potentially dramatic improvements in secure and stable prosthetic limb attachment, and corresponding improvements in amputee lifestyle, major complications can arise when the prosthetic structure encounters a mechanical load that exceeds normal design parameters. More particularly, in the event of a tensile, bending, or torsion load exceeding structural design limitations, fracture-failure can occur. Breakage of prosthesis structures such as the implanted bone anchored mounting post often requires repair by surgery. Breakage of the patient bone at or near the interface with the implanted mounting post also requires surgical repair, and reseating or replacement of the implanted mounting post may not be possible. Both of these failure modes represent traumatic and highly undesirable complications.
There exists, therefore, a significant need for further improvements in and to external or exoskeletal prosthetic devices of the type utilizing a bone anchored mounting post, wherein an improved attachment system couples the prosthetic device to an externally protruding fixator structure in a manner accommodating substantially normal patient movement and a corresponding range of normal mechanical loads, but wherein the improved attachment system includes a safety release mechanism adapted to release in response to an excess mechanical load thereby preventing undesirable fracture failures. The present invention fulfills these needs and provides further related advantages.